As disclosed in Japanese Laid-Open Utility Model Publication No. 05-009618, the present applicant has proposed a filter (fluid pressure device) for removing dust, particulates and the like contained in a pressure fluid. The filter comprises a body having ports therein for supply and discharge of the pressure fluid, a hollow case disposed on a lower portion of the body, and a filter element, which is capable of removing dust and the like, accommodated inside the case. Further, a case cover, which covers the case, is provided on an outer circumferential side of the case. A confirmation window is provided in the case cover for allowing confirmation from the exterior of the condition of the filter element inside the case.